ssl_client.cpp

/* Provide SSL/TLS functions to ESP32 with Arduino IDE
*
* Adapted from the ssl_client1 example of mbedtls.
*
* Original Copyright (C) 2006-2015, ARM Limited, All Rights Reserved, Apache 2.0 License.
* Additions Copyright (C) 2017 Evandro Luis Copercini, Apache 2.0 License.
*/

#include "Arduino.h"
#include <esp32-hal-log.h>
#include <lwip/err.h>
#include <lwip/sockets.h>
#include <lwip/sys.h>
#include <lwip/netdb.h>
#include "ssl_client.h"


const char *pers = "esp32-tls";

static int handle_error(int err)
{
#ifdef MBEDTLS_ERROR_C
    char error_buf[100];
    mbedtls_strerror(err, error_buf, 100);
    log_e("%s", error_buf);
#endif
    log_e("MbedTLS message code: %d", err);
    return err;
}


void ssl_init(sslclient_context *ssl_client)
{
    mbedtls_ssl_init(&ssl_client->ssl_ctx);
    mbedtls_ssl_config_init(&ssl_client->ssl_conf);
    mbedtls_ctr_drbg_init(&ssl_client->drbg_ctx);
}


int start_ssl_client(sslclient_context *ssl_client, uint32_t ipAddress, uint32_t port, const char *rootCABuff, const char *cli_cert, const char *cli_key)
{
    char buf[512];
    int ret, flags, len, timeout;
    int enable = 1;
    log_i("Free heap before TLS %u", xPortGetFreeHeapSize());

    log_i("Starting socket");
    ssl_client->socket = -1;

    ssl_client->socket = lwip_socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (ssl_client->socket < 0) {
        log_e("ERROR opening socket");
        return ssl_client->socket;
    }

    struct sockaddr_in serv_addr;
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = ipAddress;
    serv_addr.sin_port = htons(port);

    if (lwip_connect(ssl_client->socket, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) == 0) {
        timeout = 30000;
        lwip_setsockopt(ssl_client->socket, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout));
        lwip_setsockopt(ssl_client->socket, SOL_SOCKET, SO_SNDTIMEO, &timeout, sizeof(timeout));
        lwip_setsockopt(ssl_client->socket, IPPROTO_TCP, TCP_NODELAY, &enable, sizeof(enable));
        lwip_setsockopt(ssl_client->socket, SOL_SOCKET, SO_KEEPALIVE, &enable, sizeof(enable));
    } else {
        log_e("Connect to Server failed!");
        return -1;
    }

    fcntl( ssl_client->socket, F_SETFL, fcntl( ssl_client->socket, F_GETFL, 0 ) | O_NONBLOCK );

    log_i("Seeding the random number generator");
    mbedtls_entropy_init(&ssl_client->entropy_ctx);

    ret = mbedtls_ctr_drbg_seed(&ssl_client->drbg_ctx, mbedtls_entropy_func,
                                &ssl_client->entropy_ctx, (const unsigned char *) pers, strlen(pers));
    if (ret < 0) {
        return handle_error(ret);
    }

    log_i("Setting up the SSL/TLS structure...");

    if ((ret = mbedtls_ssl_config_defaults(&ssl_client->ssl_conf,
                                           MBEDTLS_SSL_IS_CLIENT,
                                           MBEDTLS_SSL_TRANSPORT_STREAM,
                                           MBEDTLS_SSL_PRESET_DEFAULT)) != 0) {
        return handle_error(ret);
    }

    /* MBEDTLS_SSL_VERIFY_REQUIRED if a CA certificate is defined on Arduino IDE and
        MBEDTLS_SSL_VERIFY_NONE if not.
        */
    if (rootCABuff != NULL) {
        log_i("Loading CA cert");
        mbedtls_x509_crt_init(&ssl_client->ca_cert);
        mbedtls_ssl_conf_authmode(&ssl_client->ssl_conf, MBEDTLS_SSL_VERIFY_REQUIRED);
        ret = mbedtls_x509_crt_parse(&ssl_client->ca_cert, (const unsigned char *)rootCABuff, strlen(rootCABuff) + 1);
        mbedtls_ssl_conf_ca_chain(&ssl_client->ssl_conf, &ssl_client->ca_cert, NULL);
        //mbedtls_ssl_conf_verify(&ssl_client->ssl_ctx, my_verify, NULL );
        if (ret < 0) {
            return handle_error(ret);
        }
    } else {
        mbedtls_ssl_conf_authmode(&ssl_client->ssl_conf, MBEDTLS_SSL_VERIFY_NONE);
        log_i("WARNING: Use certificates for a more secure communication!");
    }

    if (cli_cert != NULL && cli_key != NULL) {
        mbedtls_x509_crt_init(&ssl_client->client_cert);
        mbedtls_pk_init(&ssl_client->client_key);

        log_i("Loading CRT cert");

        ret = mbedtls_x509_crt_parse(&ssl_client->client_cert, (const unsigned char *)cli_cert, strlen(cli_cert) + 1);
        if (ret < 0) {
            return handle_error(ret);
        }

        log_i("Loading private key");
        ret = mbedtls_pk_parse_key(&ssl_client->client_key, (const unsigned char *)cli_key, strlen(cli_key) + 1, NULL, 0);

        if (ret != 0) {
            return handle_error(ret);
        }

        mbedtls_ssl_conf_own_cert(&ssl_client->ssl_conf, &ssl_client->client_cert, &ssl_client->client_key);
    }

    /*
        // TODO: implement match CN verification

        log_i("Setting hostname for TLS session...");

                // Hostname set here should match CN in server certificate
        if((ret = mbedtls_ssl_set_hostname(&ssl_client->ssl_ctx, host)) != 0)
        {
            return handle_error(ret);

        }
    */

    mbedtls_ssl_conf_rng(&ssl_client->ssl_conf, mbedtls_ctr_drbg_random, &ssl_client->drbg_ctx);

    if ((ret = mbedtls_ssl_setup(&ssl_client->ssl_ctx, &ssl_client->ssl_conf)) != 0) {
        return handle_error(ret);
    }

    mbedtls_ssl_set_bio(&ssl_client->ssl_ctx, &ssl_client->socket, mbedtls_net_send, mbedtls_net_recv, NULL );

    log_i("Performing the SSL/TLS handshake...");

    while ((ret = mbedtls_ssl_handshake(&ssl_client->ssl_ctx)) != 0) {
        if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
            return handle_error(ret);
        }
    }


    if (cli_cert != NULL && cli_key != NULL) {
        log_i("Protocol is %s Ciphersuite is %s", mbedtls_ssl_get_version(&ssl_client->ssl_ctx), mbedtls_ssl_get_ciphersuite(&ssl_client->ssl_ctx));
        if ((ret = mbedtls_ssl_get_record_expansion(&ssl_client->ssl_ctx)) >= 0) {
            log_i("Record expansion is %d", ret);
        } else {
            log_i("Record expansion is unknown (compression)");
        }
    }

    log_i("Verifying peer X.509 certificate...");

    if ((flags = mbedtls_ssl_get_verify_result(&ssl_client->ssl_ctx)) != 0) {
        log_e("Failed to verify peer certificate!");
        bzero(buf, sizeof(buf));
        mbedtls_x509_crt_verify_info(buf, sizeof(buf), "  ! ", flags);
        log_e("verification info: %s", buf);
        stop_ssl_socket(ssl_client, rootCABuff, cli_cert, cli_key);  //It's not safe continue.
        return handle_error(ret);
    } else {
        log_i("Certificate verified.");
    }
    
    if (rootCABuff != NULL) {
        mbedtls_x509_crt_free(&ssl_client->ca_cert);
    }

    if (cli_cert != NULL) {
        mbedtls_x509_crt_free(&ssl_client->client_cert);
    }

    if (cli_key != NULL) {
        mbedtls_pk_free(&ssl_client->client_key);
    }    

    log_i("Free heap after TLS %u", xPortGetFreeHeapSize());

    return ssl_client->socket;
}


void stop_ssl_socket(sslclient_context *ssl_client, const char *rootCABuff, const char *cli_cert, const char *cli_key)
{
    log_i("Cleaning SSL connection.");

    if (ssl_client->socket >= 0) {
        close(ssl_client->socket);
        ssl_client->socket = -1;
    }

    mbedtls_ssl_free(&ssl_client->ssl_ctx);
    mbedtls_ssl_config_free(&ssl_client->ssl_conf);
    mbedtls_ctr_drbg_free(&ssl_client->drbg_ctx);
    mbedtls_entropy_free(&ssl_client->entropy_ctx);
}


int data_to_read(sslclient_context *ssl_client)
{
    int ret, res;
    ret = mbedtls_ssl_read(&ssl_client->ssl_ctx, NULL, 0);
    //log_e("RET: %i",ret);   //for low level debug
    res = mbedtls_ssl_get_bytes_avail(&ssl_client->ssl_ctx);
    //log_e("RES: %i",res);
    if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE && ret < 0) {
        return handle_error(ret);
    }

    return res;
}


int send_ssl_data(sslclient_context *ssl_client, const uint8_t *data, uint16_t len)
{
    //log_i("Writing HTTP request...");  //for low level debug
    int ret = -1;

    while ((ret = mbedtls_ssl_write(&ssl_client->ssl_ctx, data, len)) <= 0) {
        if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
            return handle_error(ret);
        }
    }

    len = ret;
    //log_i("%d bytes written", len);  //for low level debug
    return ret;
}


int get_ssl_receive(sslclient_context *ssl_client, uint8_t *data, int length)
{
    //log_i( "Reading HTTP response...");   //for low level debug
    int ret = -1;

    ret = mbedtls_ssl_read(&ssl_client->ssl_ctx, data, length);

    //log_i( "%d bytes readed", ret);   //for low level debug
    return ret;
}